Ice storms are dangerous and destructive winter weather events that often impact the SCIPP region and other parts of the country. Freezing rain and freezing drizzle produce hazardous conditions with significant societal impacts that can last from several days to several weeks. Industries that are impacted by these events include power, transportation, aviation, insurance, and public safety. Minor glaze accumulation causes pedestrian and traffic accidents, while severe ice storms cause power outages, delays and closings of ground and air transportation, property damage, and physical injury.
SCIPP graduate student Carly Kovacik looked into whether the frequency of these storms changed during the periods 1966-1977 and 1998-2011. Those periods were associated with notable changes in global temperature anomalies related to the El Niño-Southern Oscillation (ENSO). The most notable shift in ice storm frequency between the two time periods was observed outside of the SCIPP region, over the northeast U.S., and hypothesized to be associated with changes in global atmospheric circulations. A climatology of northeast United States ice storms from 1966-2011 was then compared to phase changes of the North Atlantic Oscillation (NAO), the Arctic Oscillation (AO), the Atlantic Multidecadal Oscillation (AMO), and ENSO. Ice storm frequency was highest across the northern portion of the Northeast U.S. when El Niño conditions were present with negative AMO conditions. Ice storm frequency was highest across the southern portion of the Northeast U.S. when La Niña conditions were present with positive AMO conditions.Inconsistencies within the definition of an ice storm and ice accretion measurements were encountered and determined to hinder the accuracy of existing ice storm climatologies, though the extent is unclear.